1. Field of the Invention
The present invention relates to liquid treatment equipment for liquid treating a surface being treated of a substrate being treated and a liquid treatment method therefor, in particular relates to liquid treatment equipment suitable for improving uniformity in plane of liquid treatment and a liquid treatment method therefor.
2. Description of the Related Art
As a semiconductor device or liquid crystal display device has been required to be processed more and more finely, a liquid treatment process for manufacturing the semiconductor device or liquid crystal display device, in the place of the chemical vapor deposition process, has been frequently employed.
As an example of the liquid treatment process, a process for implementing copper plating on a surface of a wafer that is a substrate being treated is explained. In general, a process for implementing such copper plating is part of a process of forming a copper pattern in a fine trench or bia hole that is formed in advance in each portion of the wafer surface. Here, each portion of the wafer surface is one of regions formed in a large number and is a region to be a single semiconductor device (semiconductor chip).
When copper plating on the wafer surface being treated, prior to the treatment, a seed layer is formed in advance on the wafer surface. The seed layer becomes a cathode in electrolytic plating to supply electricity to a plating layer to be formed and a plating solution, and is a seed in plating.
The seed layer of a thickness of approximately from several nm to approximately 200 nm combines a copper layer of the same material with a layer of different material from a later plating layer. In view of the size relationship with the fine trench or the bia hole formed previously on the wafer surface, the seed layer is formed so as to cover a sidewall surface and a bottom surface of the trench or bia hole. While holding a periphery of the wafer on which such seed layer is formed, an electric conductor (contact) is brought into contact with the seed layer in the neighborhood of the periphery to supply electricity for plating.
The wafer thereto electricity is supplied is immersed in a plating solution bath (treatment solution bath) for the seed layer to be a cathode. In the plating solution bath, for instance an aqueous solution of copper sulfate (CuSO4) that is an electrolytic solution containing plating material is filled. In the plating solution bath, in contact with the aqueous solution of copper sulfate, an anode electrode of copper containing phosphorus is disposed. The plating is implemented by the way that fills the fine trench or bia hole previously formed on the wafer surface and furthermore covers the wafer surface with a definite thickness.
Toward the wafer surface being treated immersed in the plating solution bath, a flow of the plating solution is formed to maintain uniformity in the bath of the plating solution and to bring the plating solution containing an active additive agent always into contact with the wafer surface being treated. For this, at a portion facing the surface being treated in the plating solution bath, an ejection tube of the plating solution is disposed, at an extension that is a root of the ejection tube a pump being disposed to eject the plating solution. The additive agent is added to the plating solution to fill the fine trench or the bia hole with the plating material without leaving void, thereby forming a copper pattern of high quality.
Furthermore, usually, for instance in accordance with an increase of the plating solution in the plating solution bath due to the ejection thereof, a plating solution circulation system is formed. The plating solution circulation system recovers the plating solution overflowed from the plating solution bath and circulates the overflowed plating solution to eject again from ejection tube.
With such configurations, while maintaining uniformity of the plating solution in the bath and always supplying the plating solution containing the active additive agent in the bath, an electricity is supplied between a cathode and an anode. Thereby, copper is reduced to precipitate on the cathode that is initially the seed layer, that is, copper being formed on the seed layer as the plating.
Thus formed plating layer covering the wafer surface with a definite thickness, essentially from an efficiency requirement in the later process, is preferable to be formed with a more uniform thickness on the wafer surface. However, since power for plating is supplied from the periphery of the wafer as mentioned above, the plating layer tends to be formed thicker in the wafer periphery and thinner in a wafer center. This is because, since the seed layer is conductive but very thin, an electric resistance in a radial direction of the wafer cannot be ignored.
That is, when supplying power for plating, during reaching from the wafer periphery to the wafer center, a voltage drop occurs. When seeing a potential distribution of the surface being treated from a potential of an anode electrode, a larger potential difference occurs as goes to the periphery side. Thereby, due to the larger potential difference as goes to the periphery side, a larger electric current flows to result in promotion of the plating.
Accordingly, in the existing plating equipment, if not invoking to any countermeasure, the thickness of a film formed on the wafer surface cannot be uniform but thicker in the periphery, thinner in the center. This point must be improved (nonuniformity in plane of the film thickness).
Next, as another example of a liquid treatment process, an electrolytic polishing process will be explained in which after implementing copper plating on a surface of a wafer that is a substrate being treated, an excess plating layer is polished to remove.
In the semiconductor manufacturing process, usually, subsequent to the plating process, the plating layer is polished. Thereby, only in the fine trench or bia hole formed on the wafer surface, metal can be patterned. That is, as mentioned above, by means of the plating process, the fine trench or bia hole is filled by the metal, and furthermore the metal is plated on the wafer surface with a definite thickness including the fine trench or bia hole. Then, due to the polishing process, while leaving the metal in the fine trench or bia hole, the plating metal other than the above on the wafer surface is polished to remove. For the polishing process, mechanochemical polishing is frequently used but other method than this also can be adopted.
For the equipment for implementing such electrolytic polishing, the plating equipment is frequently diverted. One of reasons is that since the electrolytic polishing process and the plating process are opposite processes as a reaction process, a simple reversal of a polarity applying to the cathode and anode enables to realize.
When diverting the plating equipment as the electrolytic polishing equipment, power supply to the wafer surface for electrolytic polishing is implemented through the periphery thereof. In that case, removal speed of the metal due to the electrolytic polishing is larger as approaches the periphery of the wafer surface.
This is because, as mentioned above, due to the electric resistance of the metal, as approaches the periphery of the wafer surface, only a little larger voltage is generated, thereby between the opposing electrodes, for that a larger electric current is flowed to forward the electrolytic polishing. Accordingly, the metal closer to the periphery of the wafer surface is preferentially polished. When the polishing of that portion proceeds to a bottom surface of the metal layer, a power supply point and the metal surface is electrically disconnected to stop further electrolytically polishing the wafer surface.
As a result, the metal that has not been electrolytically polished and has to be removed remains on the central portion of the wafer surface. The remaining metal to be removed is necessary to be removed by a separate method.
That is, in the existing electrolytic polishing equipment, there is a problem that the metal that has to be polished to remove, without being polished, remains in particular in the neighborhood of the center of the surface being treated (presence of residual metal portion).